The PHD finger (Plant Homeodomain) module is a signature chromatin-associated protein motif. This module is present throughout eukaryotic proteomes, and mutations in the PHD fingers of many proteins are associated with cancers, immunodeficiency and mental retardation syndromes, and other genetic disorders. We previously demonstrated that a subset of PHD fingers act as high affinity binding modules for histone H3 trimethylated at lysine 4 (H3K4me3). We linked H3K4me3 to multiple different functions via its recognition by discrete PHD finger nuclear proteins, including providing the firs evidence that disrupting the read-out of a histone modification can cause an inherited human disease. Our long-term goal is to develop a comprehensive understanding of how PHD domain-containing proteins impact on chromatin dynamics and the relationship of such activities to fundamental nuclear functions and human disease processes. Here we focus on the multiple PHD domain-containing protein NSD2 (also named MMSET and WHSC1), a histone lysine methyltransferase implicated in the pathogenesis of the hematologic malignancy multiple myeloma. However, the molecular mechanism by which NSD2 regulates chromatin and the relationship of its enzymatic activity to disease pathogenesis is not well understood. Our preliminary work indicates that the primary physiologic activity at chromatin of NSD2 is dimethylation of histone H3 at lysine 36 (H3K36me2), and that NSD2 - via H3K36me2 catalysis - drives oncogenic programming in myeloma cells. In Aim 1, we propose to extend our genomic studies and determine the genome-wide distribution of NSD2 in cancer and normal cells, and investigate the role of NSD2 activity and chromatin targeting in determining the H3K36me2 chromatin landscape. We also aim to elucidate the molecular mode of action for the NSD2 PHD domains and their role in the regulation of NSD2 cellular functions. In Aim 2, we will characterize the mode of action for H3K36 methylation. We will identify proteins that preferentially recognize H3K36me2 and test the hypothesis that these proteins transduce NSD2 activity at chromatin to downstream biological outcomes. We will also explore the broader hypothesis that exquisite level of biological regulation can be achieved by subtle changes in histone methylation. The goal of Aim 3 is to identify new substrates of NSD2 using a novel chemical biological-proteomic strategy we have developed for proteome-wide discovery of functionally-relevant NSD2 substrates. The role of the most promising targets in regulation of nuclear pathways will be investigated using a combination of molecular and cellular approaches. These studies will identify new nuclear signaling pathways that are regulated by NSD2 and that may play a role in human disease. Together these studies will provide important new insights into how histone methylation regulates fundamental nuclear processes and the relationship of these activities to the pathogenesis of human diseases.